Investigate redesign of public types to unions

One of the obvious types coming to mind is `TypedResults` https://github.com/dotnet/aspnetcore/blob/c31cb17a6dc348ba66a731902922ae5bc796d2a9/src/Http/Http.Results/src/TypedResults.cs#L25

We could possible change the `Results` to support unions, so that users may provide different return types in a single union type. See example below https://github.com/dotnet/aspnetcore/blob/c31cb17a6dc348ba66a731902922ae5bc796d2a9/src/Http/Http.Results/src/ResultsOfT.Generated.cs#L24-L26

```csharp
ResultUnion, NotFound, BadRequest> GetTodo(int id)
{
if (id < 0) return TypedResults.BadRequest("Invalid ID");
if (id == 0) return TypedResults.NotFound();
return TypedResults.Ok(new Todo(id, "Buy milk"));
}
```

This issue should open the discussion for any other type as well to be rewritten in union representation - not only `TypedResults`. This may come later than NET11, but should improve the user experience.